Heretofore piers have been forced into the ground by jacks or by hammering for shoring a building foundation. Piles or piers have been driven into the ground until the pier could not be driven further with the driving equipment available at the job site. When the pier could not be driven further into the ground, it was assumed that the pier had been driven to bed rock and was sufficiently supported. However, it has been found that driven piers often are not supported by bed rock and that the foundation settles as a result of contraction and expansion of the soil formation in which the piling has been driven.
Further, changes in moisture content results in expansion of the soil which imposes forces longitudinally of the driven pier exerting uplift force through piers. Non-uniform uplift forces applied to portions of a slab or foundation often crack or damage the structure.
Rotary drilling equipment has been used heretofore for drilling wells for production of water, oil and gas. In well drilling operations core samples and chips are inspected by geologists to determine the general nature of the formation in which the well is being drilled. After the well is completed, the casing and tubing are supported by hangers at the well head.
There are several known methods and apparatus for shoring a building foundation in which a piling received within a bore adjacent the foundation provides support for the foundation. One such method and apparatus, disclosed in applicant's co-pending application Ser. No. 762,800, discloses a method and apparatus for shoring a building foundation in which a bore hole is drilled adjacent the foundation. Thereafter, a casing or pipe is lowered into the bore and a fitting, adapted for sliding along the pipe, is received thereover. The fitting is urged against a downwardly-directed portion of the foundation by a hydraulic ram until the foundation is lifted a selected amount. The fitting is secured to the pipe which is cut off below ground level and the fitting and upper portion of the pipe are covered with earth.
The disclosure in the co-pending application provides a method and apparatus for shoring a building foundation which usually includes a very stable support for the shored foundation. The piling is received in the bore which is drilled until bedrock is reached thereby permitting shoring of heavy loads on each piling and assuring that once shored, there will not be additional shifting of the foundation. Moreover, the method and apparatus disclosed in the copending application does not involve pouring concrete and is relatively inexpensive.
Although the above-described method and apparatus represents a substantial improvement over the prior art, the method and apparatus disclosed in the copending application suffers from several disadvantages. In some instances it may be necessary to drill as deep as 40-50 feet or deeper to reach a rock formation which is sufficiently stable to support the lower end of a piling after the weight of the foundation is transferred to the piling. Obtaining and transporting pipe of such length is awkward and costly. In addition, removal of the drill bit and pipe string used to drill the bore and insertion of the casing pipe therein requires more time than if the pipe string having the drill bit mounted thereon could be left in the bore and used as the piling. However, due to the expense of the commercially available bits used to drill the bore, such is not practical. Another disadvantage associated with the past method and apparatus is the wear sustained by the drill bit after a period of use.
Geographical formations vary widely throughout the United States. For example, in certain areas in central Oklahoma, the bed rock is relatively flat. When it has been determined by inspection of chips circulated to the surface of the drilled bore hole that the shaft has reached bed rock, it can be assumed that other piers supporting the same foundation will require drilling to approximately the same depth. However, in certain areas in north Texas the layer of bed rock is not flat or of uniform thickness and the depth of bore holes for piers supporting a single foundation may vary significantly.
It is a more specific object of the instant invention to provide such a method and apparatus in which the drill bit and pipe string used to drill the bore adjacent the foundation may be used as a piling for shoring the foundation.